The chief enforcer of television quality and standards at regulator Ofcom is set to leave after just five months after being forced to choose between his job and his outside work as a journalist.

As the watchdog prepares to take on greater regulation of the BBC, it has emerged that a legal wrangle broke out earlier this summer when the former Economist editor Bill Emmott was told by Ofcom that writing or speaking about national or international public policy matters would be at odds with his role as chair of its content board.

It is understood that Ofcom said that, although Emmott’s role there was part time, he was writing more than they had thought he would and that they were concerned that one of his articles may one day be used as evidence of bias or a conflict of interest in a future court case.

Sources say Emmott argued that his outside interests had been cleared when he joined in January. However Ofcom insisted his two roles, as a writer and chair of the content board, were incompatible.

The abolition of the BBC Trust at the end of the year under the terms of the new BBC charter gives the regulator new powers to oversee the corporation, including its editorial standards – a notoriously tricky area, particularly when it comes political programming.

Emmott was appointed in January when it was already suspected that the government wanted Ofcom to take on more regulation of the BBC, but since the white paper in May confirmed the move the regulator has felt under greater scrutiny.

However, the code says that “strong links with the broadcasting industry” are allowed “certain paid employment” which “may be permissible so long as it is open and accounted for and any conflict of interest is declared and discussed at a content board meeting before each relevant agenda item”.

It is not suggested that Emmott has breached any of the codes. When he took on the role – which was due to last four years – Ofcom knew of his journalism interests, including that he had previously made a documentary for the BBC about the EU called The Great European Disaster Movie.

The fact Emmott was a journalist who did not have a background as a broadcasting executive – as many who have worked for Ofcom have – was pointed to as a strength by some within the regulator, with chair Patricia Hodgson saying he had a “wealth of experience”.

It is understood that lawyers have been in discussions over the summer about the terms of his departure, which needs to be officially signed off by the Department for Culture, Media & Sport.